Even though bellow info is coming from RWS employee, this info is not official, anything might change, but right now the plan is as follows:

-DoF will have no monthly fee, this we can say with 90% certainty right now.
-Only in the event that DoF MMORTS really takes off, and we need to expand our servers, we`ll offer some sort of VIP subscription for something like 8-10$ a month.
-There will be plenty of new MMORTS content released every couple of weeks or so - quests, online campaigns, new monsters, new building and units added for your civilization. Some of these updates will be free, but majority will require VIP membership (if we do introduce one) or per-item purchase.
-Prices will be quite fair, something like 6 hour-of-gameplay new online campaign, with 3 new unit types will be priced around 5$-6$USD.
-Once we release a good deal of of such upgrades and new content (lets say in 4 months), we`ll be releasing online only expansion pack combining all the new upgrades. Prices might vary but definetly 19$ max. Few months after expansion pack is released it`ll be permanently integrated into the game and become a free update.
-There will be booster packs, similar to SAGA. But much less random, and with more variety and options. Booster packs will give player option of buying resources, more units, new unit types e.t.c at game`s website.

So in a nutshell, it`s free to play, with new free content added quite often. And even a free expansion packs down the road. But for players who really like DoF gameplay and world there will be option to spend a few bucks for new quests and units, and there will be macro VISA to Game money economy and market for really hardcore players and noobs

Should keep everyone happy, including developers. The money we`ll be collecting will mostly go towards developing new DoF MMORTS content like new quests.